1. Field of the Invention
The present invention relates to a technology for scanning the front and the back surfaces of a paper.
2. Description of the Related Art
Various approaches have been taken to reduce the size of a scanning device. For example, use of a contact image sensor (CIS), use a CIS having fewer light emitting diodes (LEDs), etc. helps to reduce the size of a scanning device.
FIG. 7A is a schematic diagram of a conventional CIS 1. FIG. 7B is a side view of the conventional CIS 1 taken along a line A-A shown in FIG. 7A. FIG. 7C is a schematic diagram for explaining scanning operation performed by the conventional CIS 1.
The CIS 1 includes a light source 11 arranged at a first end in a main scanning direction. Although not shown, the light source 11 includes three-color LEDs, i.e., a red LED that emits a red light beam, a green LED that emits a green light beam, and a blue LED that emits a blue light beam. When the CIS 1 scans a surface of a printed paper 20 by each line, each of the three LEDs emits a light beam of corresponding color in the time division manner. The light beam then passes through a light guide plate 12, so that the light beam is uniformly projected onto the printed paper 20. The printed paper 20 reflects the light beam. A rod lens array 13 collects the reflected light beam, and converges the reflected light beam onto the line sensor 14 by each pixel. A photoelectric conversion element (not shown) included in the line sensor 14 converts the received light beam into an electric signal.
As shown in FIG. 7A, because the light source 11 is arranged at the first end, the center of the CIS 1 and the center of a scanning unit (the line sensor 14) are located in different positions in the main scanning direction.
The CIS 1 scans a surface of the printed paper 20 by each line in the main scanning direction, i.e., the CIS 1 scans each line from the first pixel arranged at the first end, to the last pixel arranged at a second end opposite to the first end. As shown in FIG. 7C, when the CIS 1 finishes scanning one line, the printed paper 20 is moved over the CIS 1 in a direction perpendicular to the main scanning direction, i.e., a sub-scanning direction, for a distance equivalent to one line. The CIS 1 then scans the next line on the surface of the printed paper 20.
Japanese Patent Application Laid-open No. 2006-140902 discloses a conventional scanning device including two CISs that concurrently scan the front and the back surfaces of a printed paper. Specifically, as shown in FIGS. 8A to 9C, a first CIS 2 and a second CIS 3 are arranged in such a manner that the first CIS 2 faces the front surface of the printed paper 20 and the second CIS 3 faces the back surface of the printed paper 20. The printed paper 20 is supplied from a paper feed tray (not shown), and the printed paper is conveyed between the first CIS 2 and the second CIS 3. Then, the first CIS 2 and the second CIS 3 concurrently scan the front and the back surfaces of the printed paper 20.
FIG. 8A is a schematic diagram for explaining an arrangement of the first CIS 2 and the second CIS 3. The first CIS 2 is arranged to face the front surface, and the second CIS 3 is arranged to face the back surface of the printed paper 20. The first CIS 2 scans the front surface thereby obtaining an image of the front surface, and the second CIS 3 scans the back surface thereby obtaining an image of the back surface. The first CIS 2 scans the front surface in a forward direction, which is a direction from left to right, with respect to the front surface. The second CIS 3 scans the back surface in the forward direction, which is a direction from left to right, with respect to the back surface. In other words, scanning directions of the first CIS 2 and the second CIS 3 are opposite. Therefore, a light source 110 of the first CIS 2 and a light source 111 of the second CIS 3 are arranged at the opposite ends in the main scanning direction.
Because the light sources 110 and 111 are arranged at the opposite ends in the main scanning direction, undesired spaces indicated by two-headed arrows A are formed in the main scanning direction. As a result, the width of the scanning device increases.
As shown in FIG. 8B, the first CIS 2 and the second CIS 3 can be arranged in such a manner that the centers of the first CIS 2 and the second CIS 3 are located in the same position so that an undesired space is not formed in the main scanning direction. In this arrangement, however, the first CIS 2 cannot scan a part of the front surface of the printed paper indicated by a two-headed arrow B1, and the second CIS 3 cannot scan a part of the back surface of the printed paper indicated by a two-headed arrow B2.
FIGS. 9A to 9C are schematic diagrams for explaining the depth required for arranging the first CIS 2 and the second CIS 3. The depth is the distance in the sub-scanning direction. As shown in FIG. 9A, each of the first CIS 2 and the second CIS 3 is generally provided with a white reference portion 25 that generates white reference data to be used for shading correction performed by the scanning device. As shown in FIG. 9B, the first CIS 2 and the second CIS 3 can be arranged close to each other, thereby reducing the depth required for arrangement of the first CIS 2 and the second CIS 3. However, the white reference portions 25 are required to be arranged in such a manner that the white reference portion 25 of the first CIS 2 is not affected by a light beam emitted from the light source 11 of the second CIS 3, and the white reference portion 25 of the second CIS 3 is not affected by a light beam emitted from the light source 11 of the first CIS 2.
As shown in FIG. 9C, the first CIS 2 and the second CIS 3 can be arranged such that they are almost above/below each other. With this arrangement, the depth required for the first CIS 2 and the second CIS 3 can be reduced to the minimum, however, there is no space for arranging the white reference portions 25. Therefore, calibration data used for shading correction is stored in a memory (not shown) of the scanning device, which causes increase of costs. In addition, the calibration operation must be performed manually such that a sheet of paper is scanned and the image data is processed, which causes inconvenience to a user.
In this manner, in the scanning device shown in FIGS. 8A to 9C, undesired spaces are formed in the sub-scanning direction, and the width of the scanning device increases. Moreover, either spaces are required for arranging the white reference portions, or a memory is required for storing calibration data.
In recent years, improvements have been made in a portable computer and a portable scanning device. A user can carry a scanning device together with a portable computer, such as a laptop computer or a mobile computer. Therefore, there is a need of improving a technology for reducing the size of a scanning device.